(a) Field of the Invention
This application relates to snap-hook that includes a locking mechanism for keeping the gate of the snap-hook in a closed or locked position. The snap-hook is designed for use with a lanyard in personal fall protection.
(b) Discussion of Known Art
Snap-hooks are extremely popular in the field of fall protection. These hooks are typically attached to a lanyard that is used between a worker and a support structure or feature. One end of the lanyard is attached by way of a safety hook to the back of a harness, while the other end of the lanyard is attached to some sort of support structure, such as a crane, a section of steel or rebar, or other attachment point specifically provided for restraining a fall. These safety hooks typically include a J-shaped hook portion that includes a gate that closes the mouth of the hook in order to prevent the inadvertent release of the hook.
Because of the variety of attachment points and work condition present during an instance where the safety hook and fall arrest systems must be deployed, the actual fall path and restrain conditions are rather unpredictable. Thus, the loading on a safety hook can vary depending on what occurs during the fall. For example, some fall conditions can cause the entire load from the fall to be reacted on the gate of the hook, which is typically the weakest portion of the hook. In order to ensure that the gate does not fail, safety hooks must have gates that are capable of resisting the loads from the fall without opening into or out of the mouth of the hook.
Often a worker will loop the lanyard that is connected to the snap hook around a pipe or beam and then snap it back onto itself. This enables the worker to use items such as pipes in a pipe rack or I-beams and other structures in building steel as anchorage tie off points where no other types of anchorage connections exists.
The use of the snap is connected or snapped back around the lanyard itself has several inherent problems. The first problem is that the lanyard webbing can lie across the inside of the snap gate. A danger with the use of snap hooks is that a snap, when looped over an I-beam with the edge of the gate against the flange of the I-beam, can fail by forces on the gate which can open by the due to the action of the I-beam pressing against the gate during fall arrest. Often, the snap-hooks that are being used to hold the lanyard in the J-shaped portion of the hook are rather large in order to provide enough space in the J-shaped portion and mouth to retain the lanyard without impeding the operation of the gate.
Often, when these large hooks are laid across a flat surface, such as the top of a beam, and the gate of the hook lays against the edge of the beam, the load introduced through the hook and to the gate as the gate bears against the edge of beam is magnified by the bearing of the gate against the nose portion of the hook. This situation is particularly problematic for a snap hook, since the cooperation of the gate with the nose of the hook is essential in order to maximize the structural efficiency of the hook. If the worker falls, the force required to arrest the fall is several times the weight of the falling worker. The large size of these hooks is a detriment to the hook's ability to safely resist these forces. The length of the body of the hook creates a large cantilevered lever that must resist the fall. The bending forces to be resisted inevitable tend to bend the body of the hook. However, the hook and gate must remain closed together in order to prevent the unwanted release of the lanyard.